The adjustable pressure and vacuum limit switch valve of this invention is classified in Class 200 and Subclass 83 DP, 83 J, 83 B, 83 C, and 83 S, and the like.
Hawke, in U.S. Pat. No. 3,848,517 issued Nov. 19, 1974, discloses a pressure sensitive device for operating a switch, the device having a flexible diaphragm displaceable by a communicating high pressure fluid acting on a first diaphragm face. A piston is disposed on the second diaphragm face and is biased by a spring to move in the opposite direction. An arm is actuated by the spring, the arm actuating an electrical switch.
Hoyt, in U.S. Pat. No. 3,657,501 issued Apr. 18, 1972, discloses a pressure actuated device with concentric piston stem actuators. A simple compact system of separate pistons actuate each one of switch respectively, as there are progressive changes of fluid pressure operating on a single flexible diaphragm.
The U.S. Pat. No. 3,516,279 issued on June 23, 1970 to Maziarka discloses a spring biased pressure sensing piston arranged so that the piston assumes a position proportional to the sensed pressure. By varying the bias on the piston, the sensitivity of the piston is varied so the piston assumes a desired position at a predetermined pressure.
The U.S. Pat. No. 2,418,508 issued on Apr. 8, 1947 to Goepfrich discloses a single pressure responsive device designed to selectively operate two electrical switches at different pressure levels.
Carroll discloses in U.S. Pat. No. 1,273,577 issued July 23, 1918, an earlier valve improvement of a water controlling pressure device, embodying a flexible diaphragm transmitting fluid pressure.